Flexible pouches and pillow packages are used to wrap a multitude of different items, especially in the food industry. It is important that these packages are gastight so that food items located within the packages are protected. For certain foodstuffs, particularly fresh packaged foodstuffs, various mixtures of gases such as nitrogen, carbon dioxide and carbon monoxide are employed to maintain freshness. Some of these packaging films allow selective ingress or egress of gases to prolong the relatively short shelf life of the packaged product. Other food items such as snack foods can have lengthy shelf life periods and employ packaging films such as aluminized Mylar (Trade Mark) which are substantially impervious to gas. In other fields such as sterile medical consumables including syringes, catheters and the like, these items are usually packaged in an atmosphere of ethylene oxide, a sterilizing agent. However, current packaging techniques produce a small number of packages that have defects and therefore are not gastight. Such defects may arise from perforations in a packaging film or otherwise from the package sealing process. Food manufacturers need to identify packages with defects before they are distributed to retailers and ultimately to consumers in order that only quality produce is provided and thereby maintain customer loyalty based on product integrity.
Food packaging usually occurs at high speed with the packages passing along a production line. Often up to 800 packages per minutes pass through the production line with each package having an amount of gas located within the package.
Currently, inspectors are employed on the production line to visually identify packages that have deflated indicating that the packages have defects. These inspectors eliminate a proportion of packages with defects. However, due to the operating speed of the production line and nature of some of the defects, a substantial number of packages with defects are not identified.
In an attempt to minimise the number of defect packages not so identified, an apparatus has been developed that employs a mechanical sensor to determine if the correct pressure is located within each package. The mechanical sensor comprises two vertically spaced rollers through which packages pass. Packages that do not have defects exert a load on the rollers which is compared to a predetermined value to indicate that the package is sound. Packages with defects exert a load on the rollers that is less than the predetermined value thereby indicating an insufficiently inflated package or a leaking package.
A problem with this apparatus is that fragile or brittle foods such as potato chips located within the package can be damaged when passed through the rollers even when the package is correctly sealed. Further, food items can become positioned within the package to give a false load reading to indicate the packages are sound when they should be rejected.
An apparatus known as the WILCOMAT (Trade Mark) DL/V tests air or gas containing packages for leaks by placing a package in a sealed chamber and evacuating air from within. If the vacuum level in the test chamber fails to reach a defined minimum or if during a predetermined test period a vacuum difference is detected, the package is rejected.
Another apparatus known as the WILCOMAT (Trade Mark) MC/LFC comprises a conveyor system comprising transport pucks into which a liquid filled container is placed. The pucks are conveyed to test chambers in which a vacuum is created to a predetermined value and then after a predetermined period of time the chamber pressure is measured whereby a pressure change is indicative of the amount of liquid which leaks from a pack and is vaporized.
U.S. Pat. No. 5,513,516 describes another pressure differential measurement system for detecting leaks in packages. In this system, a package having a gas headspace is located in a sealed chamber which is evacuated to create a pressure differential between the interior of the chamber and the interior of a package. After a predetermined period of time any decay in the value of the chamber pressure is indicative of a gas leak from the package. Typically, a change in pressure of 10 millibar or greater is deemed to constitute a leak. Similar leak detection systems are disclosed in U.S. Pat. Nos. 5,042,291 and 5,029,464.
Japanese Patent Application Numbers 63078071 and 05100608 also describe leak detection systems wherein a package is subjected to a predetermined vacuum value in a sealed chamber and any decay in that value over a predetermined value of time is indicative of a gas leak from the package.
While generally satisfactory for their respective intended purposes, these differential vacuum processes are relatively slow, highly capital and space intensive and have high maintenance overheads in retaining the integrity of the vacuum chamber seals.
It is an object of this invention to overcome or ameliorate at least some of the disadvantages associated with prior art leak detection systems or to provide the consumer with a useful or commercial choice.
Throughout this specification and claims which follow, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers or steps but not the exclusion of any other integer or group of integers.